An RNG, or random number generator, is the software that produces the numbers deciding every card, reel stop and roll in an online game.
The RNG is what makes results independent. Licensed markets require it to be tested by an approved laboratory before a game goes live.
A slot spin calls the RNG the moment the button is pressed. The number returned maps to a reel position, so the result is fixed before the reels finish animating.
They are produced by a tested algorithm that is statistically indistinguishable from random and is certified by an independent laboratory before launch.
No. The result is determined at the moment of the spin. Altering it would breach the licence conditions in every market covered here.